1. Field of the Invention
This invention relates to burners and, in particular, to multiple nozzle burner construction.
2a. Technical Considerations
Continuous glass melting processes conventionally entail depositing pulverulent batch materials into a pool of molten glass maintained within a tank-type melting furnace and applying thermal energy until the materials are melted into a pool of molten glass. A melting tank conventionally contains a relatively large volume of molten glass so as to provide sufficient residence time for currents in the molten glass to effect some degree of homogenization before the glass is discharged to a forming operation. These recirculating flows in a tank-type melter may result in inefficient use of thermal energy. Conventional overhead radiant heating is inefficient in that only a portion of its radiant energy is directed towards the material being melted.
As an alternative to conventional tank-type glass melting furnaces as described above, U.S. Pat. No. 4,381,934 to Kunkle and Matesa discloses an intensified batch liquefaction process in which large volumes of batch are efficiently liquefied in a relatively small liquefaction vessel. This type of process, particularly when using intensified heat sources, produces relatively small volumes of high temperature exhaust gas. Heat from this exhaust gas may be recovered and used to directly heat a batch stream feeding the liquefaction vessel so as to improve the overall efficiency of the process.
In heating the batch material for liquefaction, it is desirable to get maximum coverage of the exposed batch within the furnace with the burners so as to use the heat efficiently. In positioning the burner to effectively heat the batch layer in a heating vessel as disclosed in U.S. Pat. No. 4,381,934, there are several factors to be considered. When the flame from a burner is too close to the batch layer, the impact of the flame may cause the layer to become unstable. As a result, the layer may slough downwardly into the vessel causing irregularities in the batch layer thickness and undesirable product. Furthermore, the resulting turbulence may result in an increase in particulate entrainment in the burner exhaust stream. Another factor to be considered is that the flame should not be aimed directly towards the upper region of the batch layer because the intense heat may adversely affect refractory materials in the vicinity. In addition, if the burner flames have to travel an excessive distance before heating the wall, thermal efficiency is lost.
To more effectively heat a batch layer, additional burners can be positioned to provide better flame distribution in the heating vessel along the batch layer. Although this would produce better flame coverage, such an alternative would complicate the heating process by requiring additional burner hardware and the corresponding tooling, maintenance, and cooling requirements.
As an alternative, a single burner with multiple outlets could be used to reduce the number of burners while maintaining an effective flame distribution. The single burner could spread the burner flames over a batch layer without requiring additional tooling or maintenance coats. The multi-nozzle burner could be positioned near the batch layer and its nozzle could be set to direct the burner flames in a sweeping action over the batch layer rather than directly at the batch layer. The resulting multi-flame sweeping burner could distribute the heat over the batch layer while reducing turbulence due to the flame impact on the layer.
It would be advantageous to have a multi-outlet burner that could distribute its heating flames over the batch layer so as to maximize transfer of heat to the batch material while reducing direct impingement by the flames on the batch and surrounding refractory.
2b. Patents of Interest
U.S. Pat. No. 3,127,156 to Shephard teaches a burner with a controllable flame position. A series of concentric pipes separate the flow of oxygen, air, fuel, and water along the length of the burner. There are two annular passages provided for the water used to cool the burner. Partitions in the annular passages ensure that the water enters at an inlet fitting and flows the length of the burner along one side before it returns along the other side of the burner to an outlet fitting. The burner has a single flame outlet at the tip of the burner.
U.S. Pat. No. 3,515,529 to Love et al. teaches a side discharge burner for use in a regenerative type glass melting furnace. Cooling fluid is introduced into a chamber extending the length of the burner. The burner is supplied with a fluid fuel, such as fuel oil, under pressure, without the introduction of pressurized air as an atomizing means. The burner includes a single outlet firing from the side of the burner.
U.S. Pat. No. 4,391,581 to Daman et al. teaches a burner for injecting fuel into passages for heated combustion air connecting the checkers with the parts of a regenerative-type glass melting furnace. A single central tube directs fuel, such as natural gas, through a water cooled jacket and out a single nozzle into the air passage tunnels. An angled tip portion is cooled by the flow of water through a cooling jacket.